This invention relates to a clutch fan drive for a vehicle engine.
A typical vehicle internal combustion engine requires the cooling capability of the engine fan for only a relatively small percentage of the total engine operating time. However, in most engine installations the fan is rotated continuously whenever the vehicle engine is operated. Since a substantial percentage of the power generated by the vehicle engine must be used to rotate the engine coolant fan, and rotation of the engine fan significantly increases the noise level around the vehicle, it is desirable to provide a clutch fan drive which uncouples the engine fan during periods when the engine coolant temperature is relatively low and the fan is not needed, and which couples the fan to the fan drive mechanism when the coolant temperature increases to a temperature level which required the cooling capability of the engine fan. Although many clutched fan drive designs have been proposed, they have received only limited acceptance, because the size of the prior art clutch mechanism substantially restricts the number of engine installations on which the drive can be fitted, and also because prior art designs generally require complicated and expensive load transmitting splines in the clutch elements and further require relatively expensive and failure-prone rotating pressure seals. Although clutched fan drives may be used beneficially with any internal combustion engine, they are particularly valuable when used with engines used to power heavy duty trucks, since these types of trucks are typically used in applications where the fan may be disconnected for substantial periods of time, thereby achieving a significant fuel savings. Furthermore, heavy duty trucks of this type are normally equipped with an air brake system, which provides a source of fluid pressure which may be used to couple and uncouple the clutching mechanism.